1. Field of the Invention
The present invention relates to an airbag device.
2. Related Background of the Invention
There has been widely used an airbag device which relieves an impact applied to an occupant and protects the occupant by sensing the impact at the time of a vehicle collision, injecting gas generated from an inflator (a gas generator) into an airbag, and deploying the bag to thereby interpose the airbag between the occupant and a vehicle body. In recent years, in order to protect the occupant from the impact at the time of the collision of the vehicle, the airbag device has been included as standard equipment in a vehicle such as a motor vehicle.
As the airbag device, in addition to the airbag device which protects a driver and an occupant in a passenger's seat, various types of airbag devices are put to practical use, for example, for protecting an occupant in a rear seat, protecting a pedestrian, protecting an occupant's head from the impact at the time of a side collision or a rolling over of the vehicle, and the like. Furthermore, a shape of the airbag is designed to fit for installation position or intended use.
Many airbag devices are configured such that a pouch shaped airbag is deployed by high-pressure gas generated from a gas generator such as an inflator, at a time of the collision of the vehicle, and impact such as collision is absorbed and relieved by the airbag, as mentioned above. In this way, the configuration for protecting the occupant from impact or the like is employed in the airbag.
The airbag device is configured such that the airbag is deployed instantaneously by the high-pressure gas which is jetted out of the inflator, and then a pressure inside the airbag is adjusted by appropriately releasing the gas inside the airbag in a stage of restraining, thereby effectively constraining the occupant.
As a method of moderately letting out the gas in the inner portion of the airbag, a technique of forming a vent hole for discharging the gas in an airbag main body has been employed. As a configuration of an exhaust portion via the vent hole, various techniques have been conventionally proposed. For example, there have been proposed an airbag device or the like in which the gas discharge is suppressed by increasing an air-flow resistance from the vent hole in the initial stage of the deployment of the airbag, and the vent hole can be fully opened in the later stage of the deployment, and an airbag which can effectively protect a head portion of an occupant in whichever of a case where the occupant fastens the seat belt and a case where the occupant does not fasten the seat belt in a configuration in which the vent hole is opened and closed by using a tether.
Furthermore, in this kind of conventional vehicular airbag device, there has been known an airbag device configured such that an inflating shape of the airbag or an inflating gas pressure (an internal pressure) in an inner portion of the airbag can be appropriately selected, while taking into consideration whether a seating position of the occupant is near the airbag or away from the airbag in order to capture and protect the occupant effectively, in the case where the airbag is deployed by the inflating gas which is jetted out of the inflator by sensing an impact of a vehicle collision. One of the airbag is referred to as a so-called accumulator-type airbag, and the other airbag is referred to as a variable displacement-type airbag.
The accumulator type airbag and the variable displacement type airbag are both constituted such that a vent hole is provided in a base cloth constructing the airbag, and an inflating gas pressure of the inner portion is adjusted by appropriately opening and closing the vent hole.
In addition, among the above-mentioned two types of airbags, the accumulator-type airbag allows the inflating gas to be discharged by opening the vent hole in the initial stage of the deployment, to thereby reduce the impact of the occupant being seated in a state in which the occupant is near the airbag, and allows the airbag to be further deployed from the initial stage of the deployment in the case where the occupant is seated while being away from the airbag, and suppresses the discharge of the inflating gas by closing the vent hole or making the opening of the vent hole small during the process of the deployment and achieves an early deployment, thereby reliably capturing and protecting the occupant having been spaced therefrom.
On the other hand, the variable displacement-type airbag is configured such that vent holes are formed in a pair of base fabrics constituting the airbag, and the vent holes are opened during the process of the deployment of the airbag by gas (inflating gas) generated by an inflator at a time of the vehicle collision. For this purpose, the variable displacement-type airbag is configured such that a pair of overlapping base cloths are joined by a separable joint and the joint can be separated by a load when the airbag deploys, and furthermore, an end portion of a vent hole cover closing the vent hole is joined by the joint near an outer peripheral portion of the airbag, and the end portion of the vent hole cover is separated from the base cloth by separating the joint so as to open the vent hole.